Aircraft air conditioning systems often employ cabin air recirculation. In such an arrangement, air is drawn from the cabin by a fan and channeled through a recirculation duct to the air conditioning apparatus where it is mixed with fresh air, and cooled for delivery to the cabin. It will be appreciated that a rupture of the recirculation duct could result in severe cabin depressurization causing passenger discomfort and/or injury. Accordingly, checking of excessive forward flow in the recirculation duct such as would result from such a rupture, is required. It will be further appreciated that fan failure could result in reverse flow through the recirculation duct. Such reverse flow also requires checking. For economy and compactness, it is desirable to achieve such excess forward and reverse flow checking by a single valve.
While check valves per se have been known in the art, none have proven to be suitable for use in checking both reverse and excessive forward flows in a recirculation duct of an aircraft air conditioning system. U.S. Pat. No. 3,861,414 to Peterson II discloses a bidirectional flow stop valve which checks in both forward and reverse directions. However, the Peterson II valve relies on a ball valve element received within a seated poppet for reverse flow checking and partially separable from the poppet for forward flow checking. The weight of such a ball valve element would render such an element unsuitable for an air conditioning system as described hereinabove where flow areas are of substantial magnitude. Furthermore, repeated engagement of such valve elements as employed in the Peterson II device, could result in rapid and substantial wear of the elements.